"It's more challenging per enemy when there are four players. Early co-op tests were just four players smashing through everything in the level, just devastating everything.

"Because these levels can be played through by one player, so you throw in three more intelligent players and it's just carnage. So the more people that you add, the more challenging each enemy gets."

Watch the Gears of War 3 campaign trailer below:

Perry also said that there are "production issues" in devoting resources for a campaign that most players would only play once or twice, and so co-operative play is a way of offsetting that.

"We did the four-player co-op and then we put in arcade mode as well, because it's about how you get people to replay the campaign," he revealed.

"There are a lot of production issues, because you spend a lot of time on a multiplayer map and people spend days in there, but with the campaign people run through it once, maybe twice and then they never see it again."

He added: "So we really thought about how we can get people to go in and replay the campaign with their buddies. In general, the ability to get you and your pack of buddies online and make you stay together was a core tenant of the project."

Gears of War 3 will be released exclusively for Xbox 360 on September 20.